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        <span>JavaScript绘制图片验证码</span>
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                <a href="/2017/10/22/validateImage/">JavaScript绘制图片验证码</a>
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                <i class="fa fa-calendar"></i> 2017-10-22
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                    <a href="/2017/10/22/validateImage/">JavaScript绘制图片验证码</a>
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                <i class="fa fa-calendar"></i> 2017-10-22
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    <ol class="post-toc"><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#步骤"><span class="post-toc-number">1.</span> <span class="post-toc-text">步骤</span></a></li><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#代码"><span class="post-toc-number">2.</span> <span class="post-toc-text">代码</span></a></li></ol>
    <div class="content-article">
        <h2 id="步骤"><a href="#步骤" class="headerlink" title="步骤"></a>步骤</h2><ol>
<li>在html中加入<code>canvas</code>标签。</li>
<li>在js中绘制一个矩形框。</li>
<li>绘制随机文字并随机颜色，随机倾斜一定角度。</li>
<li>绘制干扰线、干扰点。</li>
</ol>
<blockquote>
<p>在倾斜验证码时，倾斜的只会是画布，文字不会跟随。因此，可以把画布的起始位置移动到绘制文字的位置，然后将画布倾斜一定角度，然后再绘制文字，第一个文字绘制完成后将画布归位，继续绘制第二个文字。画布倾斜的单位是弧度。</p>
</blockquote>
<h2 id="代码"><a href="#代码" class="headerlink" title="代码"></a>代码</h2><p>HTML：</p>
<pre class="line-numbers language-html"><code class="language-html"><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>html</span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>head</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>meta</span> <span class="token attr-name">charset</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>utf-8<span class="token punctuation">"</span></span> <span class="token punctuation">/></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>script</span> <span class="token attr-name">src</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>js/demo.js<span class="token punctuation">"</span></span><span class="token punctuation">></span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>script</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>link</span> <span class="token attr-name">rel</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>stylesheet<span class="token punctuation">"</span></span> <span class="token attr-name">href</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>css/demo.css<span class="token punctuation">"</span></span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>head</span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>body</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>canvas</span> <span class="token attr-name">id</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>validate<span class="token punctuation">"</span></span><span class="token punctuation">></span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>canvas</span><span class="token punctuation">></span></span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>a</span> <span class="token attr-name">href</span><span class="token attr-value"><span class="token punctuation">=</span><span class="token punctuation">"</span>javascript:;<span class="token punctuation">"</span></span><span class="token punctuation">></span></span>换 一 个<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>a</span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>body</span><span class="token punctuation">></span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>html</span><span class="token punctuation">></span></span>
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>CSS：</p>
<pre class="line-numbers language-css"><code class="language-css"><span class="token selector">a </span><span class="token punctuation">{</span>
    <span class="token property">text-decoration</span><span class="token punctuation">:</span> none<span class="token punctuation">;</span>
    <span class="token property">height</span><span class="token punctuation">:</span> <span class="token number">30</span>px<span class="token punctuation">;</span>
    <span class="token property">width</span><span class="token punctuation">:</span> <span class="token number">200</span>px<span class="token punctuation">;</span>
    <span class="token property">display</span><span class="token punctuation">:</span> block<span class="token punctuation">;</span>
    <span class="token property">border-radius</span><span class="token punctuation">:</span> <span class="token number">5</span>px<span class="token punctuation">;</span>
    <span class="token property">margin-top</span><span class="token punctuation">:</span> <span class="token number">2</span>px<span class="token punctuation">;</span>
    <span class="token property">text-align</span><span class="token punctuation">:</span> center<span class="token punctuation">;</span>
    <span class="token property">background-color</span><span class="token punctuation">:</span> <span class="token function">rgb</span><span class="token punctuation">(</span><span class="token number">126</span>, <span class="token number">45</span>, <span class="token number">255</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token property">font-family</span><span class="token punctuation">:</span> <span class="token string">"微软雅黑"</span><span class="token punctuation">;</span>
    <span class="token property">font-size</span><span class="token punctuation">:</span> <span class="token number">18</span>px<span class="token punctuation">;</span>
    <span class="token property">line-height</span><span class="token punctuation">:</span> <span class="token number">30</span>px<span class="token punctuation">;</span>
    <span class="token property">color</span><span class="token punctuation">:</span> white<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
<p>JavaScript:</p>
<pre class="line-numbers language-javascript"><code class="language-javascript">window<span class="token punctuation">.</span>onload <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token function">draw</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">var</span> aTag <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">getElementsByTagName</span><span class="token punctuation">(</span><span class="token string">"a"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>aTag<span class="token punctuation">)</span><span class="token punctuation">;</span>
    aTag<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">.</span>onclick<span class="token operator">=</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    <span class="token punctuation">{</span>
        <span class="token function">draw</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token punctuation">}</span>


<span class="token keyword">function</span> <span class="token function">draw</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">var</span> width <span class="token operator">=</span> <span class="token number">200</span><span class="token punctuation">;</span>
    <span class="token keyword">var</span> height <span class="token operator">=</span> <span class="token number">60</span><span class="token punctuation">;</span>
    <span class="token function">drawImage</span><span class="token punctuation">(</span>width<span class="token punctuation">,</span> height<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token punctuation">}</span>


<span class="token comment" spellcheck="true">/**生成一个随机数**/</span>
<span class="token keyword">function</span> <span class="token function">randomNum</span><span class="token punctuation">(</span>min<span class="token punctuation">,</span> max<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token punctuation">(</span>max <span class="token operator">-</span> min<span class="token punctuation">)</span> <span class="token operator">+</span> min<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment" spellcheck="true">/**生成一个随机色**/</span>
<span class="token keyword">function</span> <span class="token function">randomColor</span><span class="token punctuation">(</span>min<span class="token punctuation">,</span> max<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">var</span> r <span class="token operator">=</span> <span class="token function">randomNum</span><span class="token punctuation">(</span>min<span class="token punctuation">,</span> max<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">var</span> g <span class="token operator">=</span> <span class="token function">randomNum</span><span class="token punctuation">(</span>min<span class="token punctuation">,</span> max<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">var</span> b <span class="token operator">=</span> <span class="token function">randomNum</span><span class="token punctuation">(</span>min<span class="token punctuation">,</span> max<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token string">"rgb("</span> <span class="token operator">+</span> r <span class="token operator">+</span> <span class="token string">","</span> <span class="token operator">+</span> g <span class="token operator">+</span> <span class="token string">","</span> <span class="token operator">+</span> b <span class="token operator">+</span> <span class="token string">")"</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">function</span> <span class="token function">drawImage</span><span class="token punctuation">(</span>width<span class="token punctuation">,</span> height<span class="token punctuation">)</span> <span class="token punctuation">{</span>

    <span class="token comment" spellcheck="true">//获取dom对象</span>
    <span class="token keyword">var</span> dom <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">"validate"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    dom<span class="token punctuation">.</span>height <span class="token operator">=</span> height<span class="token punctuation">;</span>
    dom<span class="token punctuation">.</span>width <span class="token operator">=</span> width<span class="token punctuation">;</span>
    <span class="token comment" spellcheck="true">//获取绘图对象</span>
    <span class="token keyword">var</span> context <span class="token operator">=</span> dom<span class="token punctuation">.</span><span class="token function">getContext</span><span class="token punctuation">(</span><span class="token string">"2d"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment" spellcheck="true">//绘制矩形框</span>
    context<span class="token punctuation">.</span>strokeStyle <span class="token operator">=</span> <span class="token string">"black"</span><span class="token punctuation">;</span>
    context<span class="token punctuation">.</span><span class="token function">strokeRect</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> width<span class="token punctuation">,</span> height<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">var</span> str <span class="token operator">=</span> <span class="token string">"0123456789abcdefghijklmnpqrstuvwxyz"</span><span class="token punctuation">.</span><span class="token function">toUpperCase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">5</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">var</span> index <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token number">35</span><span class="token punctuation">)</span>

        <span class="token keyword">var</span> size <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token number">20</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment" spellcheck="true">//绘制文字</span>
        context<span class="token punctuation">.</span>font <span class="token operator">=</span> <span class="token string">"30px 微软雅黑"</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span>fillStyle <span class="token operator">=</span> <span class="token function">randomColor</span><span class="token punctuation">(</span><span class="token number">50</span><span class="token punctuation">,</span> <span class="token number">160</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token keyword">var</span> deg <span class="token operator">=</span> <span class="token function">randomNum</span><span class="token punctuation">(</span><span class="token operator">-</span><span class="token number">45</span><span class="token punctuation">,</span> <span class="token number">45</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token keyword">var</span> x<span class="token operator">=</span>i <span class="token operator">*</span> <span class="token number">35</span> <span class="token operator">+</span> <span class="token number">20</span><span class="token punctuation">;</span>
        <span class="token keyword">var</span> y<span class="token operator">=</span>size <span class="token operator">+</span> <span class="token number">30</span><span class="token punctuation">;</span>

        <span class="token comment" spellcheck="true">//修改坐标原点和旋转弧度</span>
        context<span class="token punctuation">.</span><span class="token function">translate</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span> y<span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">rotate</span><span class="token punctuation">(</span>deg <span class="token operator">*</span> Math<span class="token punctuation">.</span>PI <span class="token operator">/</span> <span class="token number">180</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">fillText</span><span class="token punctuation">(</span>str<span class="token punctuation">[</span>index<span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">stroke</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment" spellcheck="true">//恢复坐标原点和旋转角度</span>
        context<span class="token punctuation">.</span><span class="token function">rotate</span><span class="token punctuation">(</span><span class="token operator">-</span>deg <span class="token operator">*</span> Math<span class="token punctuation">.</span>PI <span class="token operator">/</span> <span class="token number">180</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">translate</span><span class="token punctuation">(</span><span class="token operator">-</span>x<span class="token punctuation">,</span> <span class="token operator">-</span>y<span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token punctuation">}</span>
    <span class="token comment" spellcheck="true">//绘制干扰线</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">20</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

        <span class="token keyword">var</span> startX <span class="token operator">=</span> <span class="token function">randomNum</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> width<span class="token punctuation">)</span>
        <span class="token keyword">var</span> startY <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> height <span class="token operator">/</span> <span class="token number">2</span><span class="token punctuation">)</span>
        <span class="token keyword">var</span> endX <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> width<span class="token punctuation">)</span>
        <span class="token keyword">var</span> endY <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> height<span class="token punctuation">)</span>
        context<span class="token punctuation">.</span>strokeStyle <span class="token operator">=</span> <span class="token function">randomColor</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">255</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">beginPath</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">moveTo</span><span class="token punctuation">(</span>startX<span class="token punctuation">,</span> startY<span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">lineTo</span><span class="token punctuation">(</span>endX<span class="token punctuation">,</span> endY<span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">stroke</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token comment" spellcheck="true">//绘制干扰点</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">var</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">100</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

        <span class="token keyword">var</span> startX <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token number">200</span><span class="token punctuation">)</span>
        <span class="token keyword">var</span> startY <span class="token operator">=</span> Math<span class="token punctuation">.</span><span class="token function">floor</span><span class="token punctuation">(</span>Math<span class="token punctuation">.</span><span class="token function">random</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token number">60</span><span class="token punctuation">)</span>
        context<span class="token punctuation">.</span><span class="token function">moveTo</span><span class="token punctuation">(</span>startX<span class="token punctuation">,</span> startY<span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">lineTo</span><span class="token punctuation">(</span>startX <span class="token operator">+</span> <span class="token number">2</span><span class="token punctuation">,</span> startY <span class="token operator">+</span> <span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span>strokeStyle <span class="token operator">=</span> <span class="token function">randomColor</span><span class="token punctuation">(</span><span class="token number">50</span><span class="token punctuation">,</span> <span class="token number">160</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        context<span class="token punctuation">.</span><span class="token function">stroke</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

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